U.S. Pat. No. 2,993,025, granted July 18, 1961 to Alsup et al., discloses polyoxymethylene compositions stabilized with certain superpolyamides. No mention is made of incorporating the polyamide stabilizer in a thermoplastic polyurethane carrier resin.
U.S. Pat. No. 3,144,431, granted Aug. 11, 1964 to Dolce et al. discloses polyoxymethylene compositions stabilized with urethanes and polyurethanes. However, the compositions of the present invention contain a high-melting polyamide resin very finely dispersed in a thermoplastic polyurethane carrier resin.
U.K. Patent No. 1,009,883, published Nov. 17, 1965, and filed in the name of British Industrial Plastics Limited, discloses polyoxymethylene compositions stabilized by incorporating into the polymer a polymeric substance containing --CO--NH-- groups. Such polymeric substances include polyamides and polyurethanes. No mention is made of incorporating a polyamide stabilizer in a thermoplastic polyurethane carrier.
U.S. Pat. No. 4,098,843, granted July 4, 1978 to Johnson, discloses polyoxymethylene compositions stabilized with polyamides dispersed in a carrier resin, where the carrier resin can be polyethylene, ethylene copolymers with methyl acrylate, ethyl acrylate, vinyl acetate, acrylonitrile, carbon monoxide or methyl methacrylate, methacrylate polymers, acrylate polymers, copolyesters, polyether-esters, polystyrene, styrene/acrylonitrile copolymers, polyethylene oxide and mixtures thereof. No mention is made of thermoplastic polyurethanes as the carrier resin, or the unexpected and improved properties resulting therefrom.
Copending U.S. patent application Ser. No. 570,036, filed Jan. 16, 1984, now abandoned, discloses polyoxymethylene compositions having extraordinary impact resistance, i.e., a Gardner impact value (measured according to ASTM D-3029, Method G, Geometry D using a 3.6 kg (8 pound) weight and injection molded 7.62.times.12.7.times.0.16 cm (3.times.5.times.1/16 in) plaques of greater than 9 J (80 in-lb), which compositions consist essentially of
(a) 5-15 weight percent of at least one thermoplastic polyurethane, which polyurethane has a glass transition temperature of lower than 0.degree. C., and PA1 (b) 85-95 weight percent of at least one polyoxymethylene polymer, which polyoxymethylene polymer has a molecular weight of from 20,000 to 100,000, PA1 (a) greater than 15 weight percent and not more than 40 weight percent of at least one thermoplastic polyurethane, which polyurethane has a glass transition temperature of lower than -15.degree. C., and PA1 (b) at least 60 weight percent and less than 85 weight percent of at least one polyoxymethylene polymer, which polyoxymethylene polymer has a molecular weight of from 20,000 to 100,000,
the above-stated percentages being based on the total amount of components (a) and (b) only, the thermoplastic polyurethane being dispersed throughout the polyoxymethylene polymer as discrete particles, and the composition having a Gardner impact value of greater than 9 J.
Copending U.S. patent application Ser. No. 570,037, filed Jan. 16, 1984, now abandoned, discloses polyoxymethylene compositions having extraordinary toughness, i.e., a notched Izod value (measured according to ASTM D-256, Method A) of greater than 375 J/m (7.0 ft-lb/in), which compositions consist essentially of
the above-stated percentages being based on the total amount of components (a) and (b) only, the thermoplastic polyurethane being dispersed throughout the polyoxymethylene polymer as a separate phase having an average cross-sectional size in the minimum of not greater than 0.9 microns, and the composition having an Izod value of greater than 375 J/m.
The polyoxymethylene compositions disclosed in these two copending applications include compositions which can be improved by the present invention to give polyoxymethylene compositions characterized by improved hydrolytic and oxidative stability, no mold deposit, low formaldehyde odor and good mechanical properties.